console.log("2"==2);
console.log("2"===2);

console.log(+0 === -0);
var o1 = new Object();
var o2 = o1;
console.log(o1 === o2);

console.log("=============================================");

var x = NaN;
console.log(x === x);

console.log(x !== x);


console.log(null == undefined);
console.log(null === undefined);

console.log("=========================In操作符====================");
var point = {x:1,y:2};
delete point.y;
console.log("x" in point);
console.log("y" in point);
console.log("toString" in point);

var date = [1,3,4];
console.log(2 in date);
delete date[1];
console.log(date);

console.log("=========================================================");

var x;
if(x == null || x == undefined || !x){
    console.log(x);
    
}

